Fluorescent lamp starter



July 4, 1944. c. H. HoDGKxNs FLUORESCENT LAMP' STARTER Filed March 4, 1942 2 Sheets-Sheet l LIB INVENTOR C H /fa/f//VS- WQ (umm/- ATTORNEY July 4, 1944. c. H. HoDGKlNs FLUORESCENT LAMP STARTER Filed March 4, 1942 2 Sheets-Sheet 2 INVENTOR C'. H Hff/MS Amm ATTQRNEY Patented July 4, 1944 FLUORESCENT LAMP STARTER Charles H. Hodgkins, Fairfield, Conn., assignor to The Bryant Electric Company, Bridgeport, Conn., a corporation of Connecticut Application March 4, 1942, Serial No. 433,301

Claims.

The present invention relates to starting relays for iluorescent lamps and particularly to a thermal relay which automatically operates to start such lamps, and, if for any ,reason the lamp fails to start after a predetermined period of time, the relay likewise operates to disconnect the failed lamp from the source of supply and is automatically reset upon replacement of the failed lamp.

A relay of this type is shown and claimed in my copending application, Serial No. 430,887, illed February 14, 1942, which operates in the above mentioned manner, except that such relay required that it be manually reset upon replacement of a failed lamp. Under certain conditions, such for example as when a. lamp and relay are part of a fixture secured to a comparatively high ceiling, this manual resetting of the relay is a distinct disadvantage. In order to operate relays of this type, the heat-responsive element is heated by an electrical resistance heater which must rapidly heat the heat-responsive element to cause operation of the latter with attendant initiation of a discharge in the lamp; and once the lamp has started, such heater must generate just sufficient heat to maintain the heat-responsive element in a predetermined position. This accordingly imposes rather critical resistance characteristics upon the heater element, which is a further disadvantage from the standpoint of mass production of relays, since each resistance heater must be accurately tested and only those within narrow tolerance limits accepted for use.

It is accordingly an object; of the present invention to provide a thermal relay for the starting of uorescent lamps which automatically operates to disconnect a failed lamp from the source and wherein the relay also automatically resets upon replacement of the failed lamp.

Another object of the present invention is the provision of a thermal relay for starting fluorescent lamps which performs a sequential operation to start the lamp and, if for any reason the lamp has failed, the relay automatically performs a predetermined number of repetitious operations corresponding to a predetermined period of time, after which *t automatically operates to disconnect the failed lamp from the source and is automatically reset upon replacement of the defective lamp.

Another object of the present invention is the provision of a thermal relay for starting fluorescent lamps wherein a resistance heater of low ohmic value is employed to initially operate the relay, and a second resistance heater of high (Cl. 20o-122) ohmic value is utilized to maintain the relay in a predetermined position, thus eliminating the necessity for a heater element having narrow resistance characteristics.

A further object of the present invention is the provision of a thermal relay for starting fluorescent lamps which operates with ildelity to perform a sequential operation, including disconnectionof the lamp from the source of supply in the event of lamp failure, and which automatically resets itself upon replacement of the defective lamp.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawings wherein:

Fig. 1 is a sectional view of the starting relay unit of the present inventionand showing a front elevational .view of the relay itself;

Fig. 2 is a fragmentary sectional view of the relay of Fig. 1 taken at 90 to the latter and showing the normal open position of the relay prior to its operating;

Fig. 3 is a sectional view taken on the line III- III of Fig. 1;-

Fig. -4 is a sectional view taken on the line IV-IV of Fig. 1 and showing the closed circuit position of the relay;

Fig. 5 is a sectional View identical to Fig. 4 but showing the relay in its normally open position duringoperation of the lamp;

Fig. 6 is a sectional view identical to Fig. 4but showing the position of the relay in the lock-out position which the relay assumes upon failure of the lamp to start after a, predetermined number.

of repetitions operations of the relay corresponding to a predetermined period of time;

Fig. 7 is a schematic diagram of the circuit for starting a fluorescent lamp and utilizing the thermal relay of the present invention;

Fig. 8 is a sectional view of a starting relay unit showing in front elevation a modification which the thermal relay of the present invention may take;

Fig. 9 is a fragmentary sectional view of the relay as shown in Fig. 8, taken at to the latter and showin'g the normal position prior to energization of the discharge lamp;

Fig. 10 is a sectional view taken on the line X-X of Fig. 8;

Fig. 1l is a sectional view taken on the line XI-XI of Fig. 8;

Fig. l2 is a sectional view taken on the line XII-XII of Fig. 8 and showing the closed circuit position of the relay;

of the relay Fig. i3 is a sectional view identical to Fig. 12

V but showing the position of the relay during operation of the lamp;

Fig. 14 is also a sectional view identical to Fig. l2 but showing the lock-out" position which this particular modification of the present invention takes upon failure of the discharge lamp due to deactivation oi the electrodes, and

Fig. is a schematic diagram similar to Fig. '1 but showing the circuit arrangement for starting a fluorescent lamp utilizing the modification of the starting relay as shown in Figs. 8 to 14.

Referring now to the drawings ln detail, the starting relay of the present invention is shown generally at 5 in the several figures, and is housed within a metallic or plastic casing 6, together with a radio-frequency-suppressing condenser 1, both of which are connected in electrical parallel to a pair of socket terminals 8 and 9 adapted to engage a socket and which are secured to an insulating closure member I0.

The relay itself comprises a base l2 of suitable insulating material such as fiber, a phenolic condensation product, hard rubber or the like, and, as shown in Fig. i, this base is provided with an elongated opening Il for a purpose hereinafter described. A heat-responsive element in the form of a bimetallic member Il is secured at one end to the back of the base I2 and is angularLv bent to extend through the opening I3 and form a corrugation therein with its free end depending in the opening I3 and provided with a contact terminal I5.

As can be more clearly seen from Figs. 2, 4, 5, and 6, a second heat-responsive element or bimetallic member I5 of substantially the same configuration as the bimetallic member I4, is secured at one end to the front of the hase l2 and substantially parallels the bimetallic member I4 in every respect, being also provided with a contact. terminal I1 adjacent the contact terminal I5, which thus normally positions the heatresponsive elements Il and I6, together with their respective contacts I5 and I1, in spaced relation to each other. Moreover, since both heatresponsive elements are bimetallic and deflect in the same direction, the spacing therebetween remains constant with changes in ambient temperature.` An electric resistance heater element I8 oi' relatively high ohmic value is mounted on the base I2, under the corrugation formed in the bimetallic member Il, by means of a pair of rod-like conductors I9 and 20 which extend to the respective socket terminals l and 9. In addition, the conductor I8 is soldered or otherwise amxed to an eyelet or the like 22, the latterof which extends through the base I2 and is connected by a conductor 23 (Figs. 3 and 7) to one side of the condenser 1. This eyelet 22 is also rigidly secured to a metallic strip 24 disposed horizontally on the front face of the base I2 to which the heat-responsive element I6 is likewise connected. thus connecting one side of the heater It, one side of the condenser 1 and the heatresponsive element I6 together, as shown more clearly in Fig. 7. l

In a similar manner the conductor 20 is soli dered or otherwise afilxed to an eyelet 25 likewise extending through the base I2 and connected by a conductor 26 to the other side of the condenser 1, as well as to a metallic strip 21 horizontally disposed on the back of the base I2 and to the heat-responsive element Il. Thus by reference to Fig. 'I it will be noted that the heater, condenser and heat-responsive elements I4 and I6 are connected in electrical parallel with each other and to the socket terminals 8 and 8. When lthe relay unit is inserted in a socket, the heater Il is accordingly connected in a series circuit comprising an inductance element 28 and the fllamentary electrodes 29 and 30 of the discharge lamp 22.

Upon closure of a switch 32, the full voltage of the source of supply LI-L2, which may be a transformer or preferably a commercial source of potential of volts and which will be hereinafter referred to as full line voltage, is impressed across the heater I8 through lamp electrodes 29 and 20. The heater Il heats the heatresponsive element Il very quickly, causing it to deflect so that the contact I5 carried thereby engages the contact I1 carried by the heatresponsive element I6, as shown in Fig. 4. This engagement of the contacts I5 and I1 accordingly short-circuits the heater I8, forming a low resistance path in parallel with the latter and constituting a series heating circuit for the lamp electrodes 29 and 30, which thus rapidly heats the latter to maximum electron emitting temperature during the time the contacts I5 and I1 remain closed.

The heater I8 thus ceases to develop heat, with the result that the heat-responsive element Il cools and returns toward its normal position, thus interrupting engagement of the contacts I5 and I1, as shown in Fig. 5. Upon separation of the contacts I5 and I1, a high voltage surge is impressed by the inductance 28 across the preheated lamp electrodes 25 and lli, which initiates a discharge in the lamp 22. During operation of the lamp 32, the heater il is subjected only to lamp voltage and atl such voltage insuflicient heat is developed to again cause deflection of the heat-responsive element Il to the extent that the contacts I5 and I1 engage each other, withthe result that the relay 5 remains in the open position as shown in Fig. 5 during operation of the lamp I2.

If for any reason the discharge is not initiated in the lamp 22 upon initial operation of the relay 5, the latter will immediately repeat its cycle of operation, since the heater Il will again be subjected to substantially full line voltage and such repetitions operation will continue until the lamp finally starts. Should, however, the lamp 32 have failed, due to deactivation of the electrodes or similar cause, the relay 5 will continue its cycle of operation only for a predetermined number of operations corresponding to a predetermined period of time, after which the relay then operates to lock-out" the defective lamp.

Inasmuch as the heater IB is, as above noted, immediately ,subjected to substantially full line `voltage upon separation of the contacts I5 and I1 in the event the lamp fails to start, the heat developed by the heater I8 at this full line voltage is very shortly transmitted not only to the heat-responsive element I l, but also to the heatresponsive element or bimetallic member I6. As a consequence, this latter member I5 will deflect away from the base I2 at the same time that the heat-responsive element I4 defiects in the same direction in its normal operation in an cndeavor to close the contacts I 5 and I1.

"inasmuch as the heat-responsive element I4 is in closer proximity to the heater IB, there is naturally more of a time lag in the transfer of heat to the heat-responsive element I 6, which in the absence of provisions to the contrary would evenasoama v tually result in the element I4 overtaking the element I6 with closure of the contacts I5 and I1 and further useless repetitious operation of the relay in a futile attempt to start the defective lamp 32. To prevent this, a stop 34 is secured by an eyelet or the like 36 to the base I2. As shown in the several figures, this stop 34 is Consequently, with repetitions eperauonof the relay for a predetermined number oftimes corresponding to a predetermined period of time and attendant deflection of the heat-responsive elements I4 and I6 in the manner above stated, the heat-responsive element I4 engages the stop 34, as shown in Fig. 6, which thus prevents its contact I5 from engaging the contact I1 carried by the heat-responsive element I6 and shortcircuiting the heater I8. The latter accordingly continues to receive full line voltage, maintaining the defective lamp 32 in a "locked-out condition, thereby preventing futile operation of the relay and annoying flickering of the lamp. When the defective lamp is replaced, the circuit is naturally broken, causing the relay 5 to automatically assume its normal position, as shown in Fig. 2, due to cooling of the heat-responsive elements I4 and I6, thus placing such relay again in condition for its customary cyclic operation.

It will thus 'be seen from the foregoing that a thermal relay for starting fluorescent lamps is herein provided which is simple in operation and economical to manufacture. provided with normally open contacts which are closed to initially connect the lamp to a source of supply, with closure of such contacts being controlled by a resistance heater. Inasmuch as such heater must not develop sufficient heat to cause closure of the contacts during operation of the lamp, its resistance characteristics must be confined to rather restricted limitations. Under certain conditions it may also be desirable to provide the thermal relay with normally closed contacts so as to decrease the time lag between closure of the switch and starting of the lamp.

The present invention also contemplates a relay of this latter type, and such modification is shown in Figs. 8 to 15, inclusive. The relay shown generally at 55 is housed within the casing 56, together with the condenser 51, and socket terminals 58 and 59 are carried by the closure member 60 in the same manner as previously described. The base member 62 is also provided with an opening 63 for the same purpose as in the previously described embodiment. A heatresponsive element in the form of a bimetallic member 64 and practically identical to the element I4 in Fig. 1 is likewise secured at one end to the back of the base 62, which depends downwardly in the opening 63 and is provided with a contact 65 at its lower end.

As shown more particularly in Fig. 9, this contact 65 normally engages a contact 66, the latter of which is carried by a bimetallic stationary contact arm 61 extending angularly in the opening 63 and secured at one end by means of a rivet or the like 68 to the base 62. Another bimetallic stationary contact arm 69 is securedto a bracket 10, the latter of which is provided with an angularly disposed portion so as to position the an- The relay isprovided with a detent projecting into an openchored end o! the bimetallic contact arm 69 in spaced relation to the base member 62. This bimetallic arm 69v is provided with a contact terminal 12 at its free end and disposed in juxtaposition to the contact terminal 65 carried Iby the bimetallic element 64. As in the previously described embodiment, a heater element shown generally at 13 is disposed in the corrugation formed in the bimetallic element 64. This heater element, however, differs somewhat from that previously described in that it is formed by two resistance heater elements, as shown more particularly in the schematic diagram of Fig. 15.

By reference to this latter figure, it will 'be .noted that one such resistance heater 14 is of relatively low ohmic value, whereas the inner surrounded resistance heater element 15 is of relatively high ohmic value. One end of both resistance heaters 14 and 15 is connected by a conductor 16 to the socket terminal 58. This conductor 16 is also soldered or otherwise affixed to an eyelet or the like 11 passing through the base 62 and through the bracket 10, which thus connects the bimetallic member 69 with one end of each of the electric resistance heaters 14 and 15, as well as to the socket terminal 58. The opposite end of the heater 14 is connected by a conductor 18 to the bimetallic stationary contact arm 61, while 4a conductor 19 connects the remaining end of the high resistance heater element 15 to the socket terminal 5,9. An eyelet 80 extending through the base 62 is soldered or otherwise secured to this conductor 19, and the bimetallic element B4 is connected by this eyelet 8l! to the heater element and socket terminal. The condenser 51 is connected by conductors 82 and 83 to the eyelets 11 and 80, which thus connects the condenser 51 in parallel with the high resistance heater element 15 across the socket terminals 58 and 59.

By reference now more particularly to Fig. 9.

will be noted that in the open circuit position of the switch 33, in the relay of this particular modication the contact terminals and 66 are normally in engagement with each other. Inasmuch as both such contacts are carried by the bimetallic elements 64 and 61, respectively, changes in ambient temperature are thereby compensated so that under all ambient temperature conditions the contacts 65 and 66 remain in engagement with each other. Upon closure of the switch 33 as shown in Fig. l5, the cathodes 29 and 30 of the lamp 32 are supplied with substantially full line voltage through a circuit which extends from one side of the line LI through inductance 28 to the lamentary cathode 29, and thence to the socket terminal 58 through conductor 16, low resistance heater element 14, conductor 18, thence through normally closed contacts 66, 65, carried respectively by the bimetallic\elements 61, 64, to socket terminal 59 and thence through illamentary electrode 39, back through switch 33 to the opposite side of the line L2. Resistance heater 14 being of relatively low ohmic value quickly generates heat, which causes bimetallic member 64 to deflect away from stationary bimetallic contact arm 61, thereby interrupting the series heating circuit for the lamentary lamp electrodes 29, 30. The time required to heat the heater element 'I4 prior to deflection of the bimetallic member 64 is sufficient to preheat the filamentary electrodes 29, 38 to maximum electron emitting temperature.

- Upon separation of the contact terminals 65,

66 a high voltage surge is produced by the -inductance element 28 in the same manner as previously described, with the result that a discharge is initiated in the lamp 82 between the preheated electrodes. Opening of the contacts 85, 86 also interrupts the ilow ot current to the low resistance heater 14 and at the same time removes the substantially short-circuit condition previously existing with respect to the high resistance element 15, so that this latter is now in circuit during operation of the lamp 32 and is thus subjected to lamp voltage which is of a lower order of magnitude than line voltage to which the heater element 'I4 was previously subjected. At lamp voltage sulcient heat is generated by the high resistance heater 15 which is tranmitted to the bimetallic member t to maintain the latter' in an open circuit relationship with respect to bimetallic contact arm El', so that the relay contacts assume the position as shown in Fig. i3.

Should, however, the lamp 32Y fail to start on the first separation of the contacts 65, 66, the high resistance element will immediately be subjected to linevoltage and the resultant heat generated thereby will cause movable bimetallic member 8E to deilect still further away from the base 62 until it engages stationary contact arm 59, as shown in Fig. l2. This will establish a series heating circuit i'or the fllamentary lamp electrodes 29 and 39 directly from the socket terminal 58, through conductor 16 to the bimetallic member 69 and the contact terminal 12 carried thereby, to the contact terminal 65 carried by the bimetallic member 64, and thence by means of conductor 19 to the other socket terminal 59, thus again completing the series heating circuit for the filamentary electrodes 29 and 30.

Engagement of the contact terminals 65, 12 short-circuits the high resistance heater 15, and since the conitacts 65, 88 are open so that no current is received by the low resistance heater 1l, no heat ls generated, and movable bimetallic member 64 will cool and begin to restore itself to its normal position. The series heating circuit for the illamentary lamp electrodes 29, 30 will therefore be again interrupted and a high voltage surge from the inductance element 28 again impressed upon the preheated electrodes, thus initiating the discharge in the lamp 32. When the lamp starts, high resistance heater element 15 will then be subjected to lamp voltage and will generate sutiicient heat to maintain movable bimetallic contact member 64 in the open circuit position between the two stationary contact arms 81 and 69, as shown in Fig. 13.

In order to cause the relay 55 to lock-out" the lamp in the event the latter has failed due to deactivation of the electrodes or similar cause, as hereinbefore described, this modification is likewise provided with a stop 84 which is likewise carried by the base 62 and is bent so as to be engaged by the contact 55 carried by the movable bimetallic member 6I. For example, if the lamp l2 fails to start after a predetermined number of repetitious operations of the relay 55 corresponding to a predetermined period of time, the high resistance heater 15 will be subjected to line voltage between each attempted operation of the relay 55 and there will be an increasing rise in temperature developed. This increased temperature will cause movable bimetallic member 8l to deflect further away from the base 52. The location of stationary bimetallic contact arm 69 is such that it is also iniluenced by the generated heat and, being bimetallic,'will also move away from the base 52.

As a consequence, movable bimetallic contact member 84 will continue to deilect along with stationary bimetallic contact arm 69 away from the base 62 until the contact terminal 85 carried by the movable bimetallic member 64 engages the stop 84. Further deflection of the bimetallic member 84 is thus restrained, but stationary bi metallic contact arm 69 is free to continue its deflection away from the base so that it remains beyond a contact making position with the now restrained movable bimetallic member 64, with the relay assuming the position as shown in Fig. 14. The high resistance heater 15 is then continuously subjected to line voltage, and this open circuit condition for the lamp 32 is maintained. Moreover, further repetitions operation of the relay 55 is prevented as Well as flickering of the failed lamp 32. When, however, the defective lamp 32 is replaced, both bimetallic members 6d and t@ cool and return to their normal position, as shown in Fig. 9, ready for initial operation to start the replaced lamp 32 in the manner as above noted.

Accordingly, by providing this modification with two electrical resistance heaters, one of low ohmic value and the other of high ohmic value, it is unnecessary that the range of resistance characteristics of the heaters be as limited as in the case oi the single resistance heater element Iii, as shown in the previously described embodiment, which acordingly prolongs the useful life of the two resistance heater elements in comparison with that of the single heater elcment shown in the relay of Fig. l.

It thus becomes obvious to those skilled in the art that a starting relay for a fluorescent lamp is hel ein provided which operates with fidelity to start the lamp. Moreover, such relay performs its repetitions operation until a discharge is ultimately initiated in the lamp. Ii', however, the lamp is defective, such relay automatically operates 1o lock-out the failed lamp so as to prevent needless repetitious operation of the relay in a futile attempt to start a defective lamp; and upon replacement of such defective lamp, the relay automatically returns to its normal position preparatory to performing its normal cyclic operation to start the lamp.

In addition, the necessity for a heater element having resistance characteristics within a very narrow range may be eliminated, as in the present invention, by the provision of separate heater elements, one having a relatively low homic value for quick heating of the relay for starting purposes, and the other heater being of relatively high ohmic value so as to generate just sufficient heat to maintain the relay in a predetermined position during operation of the lamp.

Although several embodiments of the present invention have been shown and described, it is to be understood that many other modications thereof may be made without departing,1 from the spirit and scope of the appended claims.

I claim:

l. A relay for starting an electric discharge lamp comprising a base, heat-responsive means carried by said base in parallel spaced relation thereto, an electric heater disposed in heat transfer relation to said heat-responsive means for causing deflection of the latter upon the accumulation of heat therein, circuit-controlling means including a bimetallic element disposed in substantially parallel superimposed position relative to said heat-responsive means and operable to control a circuit to said lamp in response to normal deflection of said heat-responsive means due to heating and coolingr of the latter, and means -means from deflecting sufficiently to operatesaid circuit-controlling means.

2. A relay for startingv an electric discharge lamp comprising a base, heat-responsive means carried by said base in parallel spaced relation thereto, an electric heater disposed beneath said heat-responsive means for causing deflection of the latter upon the accumulation of heattherein, circuit-controlling means including a bimetallic element disposed in substantially parallel superimposed position relative to said heat-responsive means for heating by said electric heater, and o'perable to control a circuit to said lamp in response to normal deflection of said heat-responsive means due to heating and cooling of the latter; and a stop carried by said base and projectin-g into the path of oleecte'd movement oi 1 said heat-responsive means and engageable by. u

the latter upon the application of substantially full line voltage to said heater for a predetermined.r period of time to restrain said heat-responsive means from deflecting suiliciently to operate said circuit-controlling means.

3. A. relay for starting an electric discharge lamp comprising a base, heat-responsive means carried by said base in parallel spaced relation thereto and provided with a contact, an electric heater disposed in heat-transfer relation to said heat-responsive means for causing deflection of the latter upon the accumulation of heat therein,

a normally stationary bimetallic member disposed i in substantially parallel superimposed position relative to said heat-responsive means and provided with a contacet adjacent the contact carried by said heat-responsive means 'and operable to deflect in the same direction as said heat-responsive means upon the application of a potential to said heater for a predetermined period of the latter upon the application of substantially line voltage to said low resistance heater, a pair of contacts normally completing a circuit to said lamp andto said low resistance heater and operable to interrupt said circuit upon. deilection ot said heat-responsive means, a comparatively high resistance heater element also in heattransfer relation to said heat-responsive means and subjected to lamp voltage upon interruption of the circuit to said low resistance heater and normally operable to maintain said heatresponsive means in a. deflected position to prevent said contacts from again completing a circuit to said low resistance heater during operation of said lamp, and a stop carried by said base and disposed in the path of deilccted movement of said heat-responsive means to restrain deflection of the latter and prevent re-establishment of a circuit to said lamp and to saidv low resistance heater upon the application of substantially line voltage to said high resistance heater for a predetermined period of time.

5. A relay for starting an electric discharge lamp comprising a base,'heatresponsive means carried by said base in parallel spaced relation thereto, a comparatively low resistance electric heater in heat-transfer relation to said heatresponsive means for causing rapid deflection of the latter upon the application of substantially line voltage to said low resistance heater, a pair of normally engaged contacts completing a circuit to said lamp and to said low resistance heater and operable to interrupt said circuit upon dit time, said contacts being operable to control a circuit to said discharge lamp in response to normal deflection of said heat-responsive means due to heating and'cooling of the latter, and means disposed in the path of deflected movement of said heat-responsive means and engageable by the latter upon. the application of substantially full line voltage to said heater for a predetermined period of time to restrain said heatresponsive means from deflecting suillciently to cause its contact to engage the contact carried by said normally stationary bimetallic member and completing a circuit to said lamp when said bimetallic member is in a dellected position due to they accumulation of heat therein from said heater.

4. A relay for 'starting an electric discharge lamp comprising a base, heat-responsive means carried by said base in parallel spaced relation thereto, a comparatively low resistance electric heater in heat-transfer relation to said heatv responsive means for causing rapid deflection of deflection of said heat-responsive means, a bimetallic element carried by said base in substantially parallel superimposed lrelation with respect to said heat-responsive means and provided with a Contact normally disposed in spaced relation with one of said pair of contacts and operable to deflect in the same direction when heated as said heat-responsive means, a comparatively high'resistance electric heater connected to the contact carried by said bimetallic element and in heat-transfer relation with said heat-responsive means and subjected to lamp voltage upon separation of said pair of contacts for maintaining said heat-responsive means in a predetermined positionduring operation of said lamp, said ,high resistance heater being operable to heat said heat-responsive means and cause engagement of one of said pair of contacts with the contact carried by said bimetallic element upon the application ofsubstantially line voltage thereto due to failure of said lamp to start to cause repetitious operation of said relay until a discharge is initiated in said lamp, and a stop carried by said base and disposed in the path of deflected movement of said heat-responsive means to restrain dection of the latter and prevent engagement of one of said pair of contacts with the contact carried by said bimetallic member when the latter is in a deected position due to heating by said high resistance heater by the application of substantially line voltage to the latter for a predetermined period of time.

CHARLES H. HODGKINS. 

